1. Field of the Invention
The present invention relates to a numerical control system having a plurality of controllers, and more particularly to a numerical control system having controllers for reading, decoding, and executing numerical control commands.
2. Description of Related Art
Numerical control systems generally have one functional arrangement for reading, decoding, and executing numerical control commands to control a plurality of axes. There has also been employed a numerical control system having a plurality of such functional arrangements for controlling a numerically controlled multiple-head lathe or the like which has a plurality of spindles. Such a numerical control system is essentially in the form of two numerical control apparatuses combined with each other, one for controlling a first spindle, an X1 axis, and a Z1 axis and the other for controlling a second spindle, an X2 axis, and a Z2 axis.
While the above numerical control system can control a numerically controlled lathe having two spindles, since it is merely a combination of two numerical control apparatuses, it suffers the following problems:
First, the numerical control system has an unbalanced processing capability. Although there is no problem when the task of the processor of one of the numerical control apparatuses and the task of the processor of the other numerical control apparatus are in equilibrium, i.e. each of the processors has the capacity to handle its task at roughly the same rate, when these tasks are brought out of equilibrium, the processors do not have the ability to accept and process tasks from another processor which is overtasked even though the processors may have the capacity to do so.
Secondly, the two numerical control apparatuses cannot access each other's data. The numerical control system has two functional arrangements, but the lathe which is to be controlled is a single machine. Even under conditions where the numerical control apparatuses are to operate on the same data, they are unable to do so because, they cannot access each other's data. The numerical control system therefore requires memory units which would otherwise be unnecessary, and the system cannot perform flexible control. Communication ports or the like are also required by the numerical control system to eliminate the above drawback.
Thirdly, the numerical control apparatus must be provided with common peripherals such as a CRT/MDI unit, a floppy disk, etc.